Thermal Mixed Lubrication Analysis Of Cylindrical Roller Bearings

Based on the theory and experiment,mixed lubrication problems in cylindrical roller bearings were investigated in this paper.Four parts are included: A thermal mixed lubrication model for finite line contact in cylindrical roller bearings was established with non-Newtonian fluid;The wear behavior under thermal mixed lubrication was analyzed;Analysis of dynamic mixed lubrication in cylindrical roller bearings was carried out.Lubrication performance of cylindrical roller contact pair was studied experimentally during start-up and shut-down.Firstly,considering the elastic-plastic deformation of rough peak,a non-Newtonian thermal mixed lubrication model for finite line contact was established based on the average flow model.Effects of surface pattern parameter and surface hardness on the lubrication performance in cylindrical roller bearings were studied.Results show that,under mixed lubrication conditions,the lubrication condition at the end of the roller is worse than that in the middle of the roller.When the surface pattern parameter is 1.0 and the ratio of the hardness to the elastic modulus is 0.01-0.03,the lubrication performance of cylindrical roller bearings is the best.In addition,when both the surface pattern parameter and the surface hardness are considered,the dominant positions for the two factors are different.Secondly,coupling the non-Newtonian thermal mixed lubrication for finite line contact with the Archard's wear model,the wear model under thermal mixed lubrication was established.Effects of the wear length,the surface hardness and the rough peak radius on the wear and lubrication performance were analyzed.Results show that,the wear depth at the end parts of the roller is the largest.With the increase of the wear length,the lubrication state in the middle part of the roller is improved to some extent,but the lubrication state at the end parts of the roller deteriorates.When the surface hardness is high,the wear depth can be reduced,but the contact pressure of the rough peak is high.When the surface hardness is small,the wear is aggravated and the lubrication condition at the end parts of the roller deteriorates.When the radius of the rough peak is small,the wear depth increases and the film thickness at the end parts of the roller decreases.Thirdly,the dynamic non-Newtonian thermal mixed lubrication model for finite linecontact between a roller and an outer ring was established in cylindrical roller bearings.Effects of the environment viscosity of the lubricating oil,the maximum Hertzian pressure,and the surface roughness on the lubrication state for roller-outer ring contact pair were studied during start-up and shut-down.Results show that,the minimum film thickness in the deceleration stage is larger than that in the acceleration stage at the same speed during start-up and shut-down.Moreover,the higher the environment viscosity of the lubricant and the maximum Hertzian pressure,the larger the difference of the minimum film thickness between the acceleration and deceleration stages.However,the influence of surface roughness on the difference of the minimum film thickness between the acceleration and deceleration stages is not obvious.Finally,the influence of the surface roughness of the roller and acceleration on the shape and thickness of the film during start-up and shut-down was studied experimentally with the optical interferometry technology.Results show that,the bigger the surface roughness of the roller,the larger the film thickness in the acceleration stage and the early stage of the uniform speed stage,but the smaller the film thickness after the oil film stabilization and at the deceleration stage.The larger the surface roughness of the roller,the larger the fluctuation of the film thickness along the axial direction of the roller,but the fluctuation of the film thickness along the axial direction decreases with the increase in the film thickness.The acceleration affects the film thickness when the oil film is unstable.As the speed is same,at the acceleration stage,the larger the acceleration,the thinner the oil film.Whereas at the deceleration stage,the larger the acceleration,the thicker the film thickness.However,when the oil film is stable,the film thickness for different acceleration is nearly the same.During the whole start-up and shut-down cycle,the film thickness in the acceleration stage is always less than that in the deceleration stage for the same speed,which is coincident with the theoretical results.